Electrical power distribution systems often include overhead electrical power distribution lines mounted upon poles by a wide variety of mounting structure. Other distribution systems include underground distribution lines in which protected cables run under the ground surface. It is often necessary to take phase-to-phase voltage measurements across transmission lines while testing for induced or live power lines or equipment.
Known high voltage safety line detectors, meters and testers comprise high resistance probes connected in series with a calibrated panel meter to read the voltage across the phase-to-phase or phase-to-ground terminals. They are designed for use as safety tools by high voltage line maintenance workers to verify the status of the line or equipment as nominal, induced or de-energized. Known devices for providing such measurements include contact type and non-contact type. With contact type a reference probe or transmitter and a meter probe or receiver are connected in series with a cable as the loop is closed with load terminals.
Phasing and phase angle measurement on utility grid lines is critical for rapid load balancing, identifying faulty circuits, and maintenance of the grid lines. Even though feeder circuits are designed to be well balanced in the initial deployment, one of the phases may turn out to be more heavily loaded than others, leading to load imbalance conditions. Phasing meters facilitate the rebalancing of the phases and provide for rapid maintenance and restoration of clean grid systems in the field.
The high voltage detection and phase angle measurements on AC high voltage electrical lines, up to 700 kV, are done in close proximity to a high 50 Hz/60 Hz field. This results in inaccurate measurements due to interference. Known meters do not incorporate procedures to eliminate this interference.
Also, phasing meters are used in outdoor locations where the meter can be affected by high frequency electromagnetic interference (EMI). The effect of this interference will be more severe during low voltage detection. Advantageously, the interference must be suppressed before entering meter printed circuit boards and provide noise free signals for processing. Known meters do not incorporate circuits to fully eliminate such interference.
The present disclosure is directed to improvements in high voltage phasing voltmeters.